What it cost to engineer a marine alternator regulator
Total invested
$38,354
Sales to date
$1,511
Net loss
$36,843
Hours of my labor
4,314
Years
4.2
Hours per day
2.8
Where the money went
Show as a table
| Category | Amount | Share |
|---|---|---|
| Circuit boards, parts and materials | $19,497 | 50.8% |
| Contract design help | $11,939 | 31.1% |
| Training and reference | $2,415 | 6.3% |
| Test equipment | $1,630 | 4.2% |
| AI development tools | $1,554 | 4.1% |
| Website, hosting and software | $1,043 | 2.7% |
| Shipping, banking and trade shows | $277 | 0.7% |
Spend by month
Itemised months only - March 2025 onward.
What the Regulator cost to build
| Item | Qty | Cost |
|---|---|---|
| Circuit board, landed* | 1 | $86.16 |
| Wooden case, Base and Wall Dock | 1 | $30.00 |
| Alternator current sensor, 300 A hall clamp | 1 | $11.00 |
| Digital temperature sensors, M4, M5 and M8 ring lug | 3 | $6.45 |
| Mounting hardware: stainless screws and washers | 7 + 3 | $2.39 |
| P and N alternator configuration jumper | 1 | $1.56 |
| Heat-shrink labels for the four data cables | 4 | $0.04 |
| Bulkhead drilling template | 1 | $0.04 |
| Box and packing materials | 1 | $0.00 |
| Felt tape wall bumpers | set | — |
| Outbound postage | $16.39 | |
| Card and payment processing | $11.61 | |
| Price, introductory promotion | $390.00 | |
| Profit per board | $224.36 |
* V6 value. V9 is not costed yet and is going to be more expensive.
PCB cost per board vs. quantity
Works cost, before freight and dutyLanded cost per board
The curve flattens after fifty. Going from fifty boards to a hundred saves $3.47 a board and roughly doubles the cash committed to a single run, from $4,308 to $8,149. Fifty is the run size the costing argues for.
Show the full build-up
| Per board | 5 | 10 | 50 | 100 |
|---|---|---|---|---|
| Bare board | $7.37 | $4.37 | $1.97 | $1.40 |
| Components | $42.93 | $42.41 | $42.07 | $42.00 |
| Assembly labor | $29.89 | $16.15 | $5.23 | $3.57 |
| Setup and tooling | $16.67 | $8.33 | $1.83 | $1.08 |
| Inspection | $3.26 | $2.45 | $0.97 | $0.57 |
| Packaging | $0.10 | $0.05 | $0.01 | $0.00 |
| Works cost | $100.22 | $73.76 | $52.09 | $48.62 |
| Freight | $15.85 | $15.85 | $15.85 | $15.85 |
| Import duty | $35.08 | $25.82 | $18.23 | $17.02 |
| Landed per board | $151.14 | $115.42 | $86.16 | $81.49 |
| Cash for the whole run | $756 | $1,154 | $4,308 | $8,149 |
Where the board money goes, at a run of fifty
Components are the whole story, and they are a line item that doesn't move much with run size. $40.80 of the $42.07 is stock bought ahead in bulk and drawn down run by run; ten parts account for 63% of it. Everything else on the chart - the labor, the tooling, the inspection - is a flat fee divided by however many boards are in the run, which is why a run of five costs twice what a run of fifty costs.
Where the time went
Engineering + educationMarketing + business
Estimated, but with high confidence. Tracking system was not yet running.
Codebase size - AI effect
Net lines of source across the firmware, the cloud app and backend, the website and docs, and the iOS app.
Regulator firmwareCloud appCloud backendWebsite and docsiOS app
AI spend, cumulative
Tokens per month
Same time axis as the chart above, so the two line up. The session log only starts 17 June 2026.
Tokens run
Lines added per month
Regulator firmwareCloud appCloud backendWebsite and docsiOS app
Show as a table
| Month | Regulator firmware | Cloud app | Cloud backend | Website and docs | iOS app | Total |
|---|---|---|---|---|---|---|
| 2024-04 | 1,078 | 0 | 0 | 0 | 0 | 1,078 |
| 2024-07 | 1,078 | 0 | 0 | 0 | 0 | 1,078 |
| 2024-10 | 3,084 | 0 | 0 | 0 | 0 | 3,084 |
| 2025-01 | 7,777 | 0 | 0 | 0 | 0 | 7,777 |
| 2025-04 | 4,796 | 0 | 0 | 0 | 0 | 4,796 |
| 2025-07 | 11,166 | 411 | 0 | 0 | 0 | 11,577 |
| 2025-10 | 19,111 | 411 | 0 | 0 | 0 | 19,522 |
| 2026-01 | 25,895 | 7,013 | 0 | 0 | 0 | 32,908 |
| 2026-04 | 47,309 | 7,087 | 2,731 | 27,649 | 0 | 84,776 |
| 2026-07 | 114,302 | 7,551 | 6,265 | 90,371 | 1,599 | 220,088 |
| 2026-08 | 132,591 | 7,492 | 7,471 | 102,401 | 1,691 | 251,646 |
AI Costs
Token retail value
$13,925
Actual spend
$512
Subscription savings
$13,413
AI subscriptions paid, by month
Which plans, over time
Which models ran the work
Tracking this only began in June.
Opus 4.8Fable 5Opus 5Sonnet 5Haiku 4.5
Timeline
X Engineering
AI
Mar 2019
X Engineering founded A mechanical engineering consultancy, working on diesel engine development.
Aug 2019
An Arduino starter kit Bought on Amazon.
Jul 2022
The kit gets opened Ran the blink sketch. Project clock starts here.
Mar 2023
Parts start arriving Three orders to Marlin P Jones inside two weeks, $535 of components.
AI industry
GPT-4 OpenAI, 14 March 2023.Jun 2023
First regulator prototype A daughter board on a Heart InCharge regulator: digital pot under Arduino control
Sep 2023
Joined The Hardware Academy And met the freelancer who did the early hardware design.
Nov 2023
Second prototype The first breadboard regulator built entirely from basic parts. An H-bridge drove PWM into the alternator field
Jun 2024
First custom circuit board ordered From PCBWay.
Feb 2025
X Engineering
First AI subscription ChatGPT, $20, on 16 February 2025. Work moves to copy and paste with a browser LLM.Mar 2025
Boards move to JLCPCB First order 18 March 2025. Forty-seven more since.
Apr 2025
X Engineering
Claude subscriptionMay 2025
AI industry
Claude Code generally available from AnthropicMar 2026
V9 boards ordered
X Engineering
Claude Code adopted, development changes slopeMay 2026
First regulator sold
AI Assisted Measurement Methods
| Money | Copilot tracks all transactions, Claude pulls and classifies expenses weekly. |
| Time | Customized instance of ActivityWatch. |
| Code/Tokens | Standard GitHub workflow makes this one the easiest. |
Last run 26 August 2026.